American Standard Yellow Ballcock

I have an American Standard toilet with a yellow plastic ballcock. It is sort of kidney-shaped, with what appears to be some kind of screw-top on top of it. I can't seem to find any reference to it online.

Problem is ... It doesn't seem to want to shut off properly, and sometimes continues flowing into the overflow tube.

Any ideas on a repair?

They were so troublesome that A/S stopped using them. You can replace it with a fluidmaster 400A or a Corky Quietfill.

fill valve

The only thing I do with them is throw them away, often as soon as I install the toilet so I do not get a call back saying that it will not shut off.

Ok ...

Being a new homeowner, not sure about how to identify the exact toilet model to buy a replacement for it ... how do I identify the model?

fill valve

You don't have to. You use the Fluidmaster 400A, or any generic fill valve, other than the 1B-1X made for low profile toilets which you do not have.

The two most common refill valves are Fluidmaster and Korky. Neither costs more than $10, and they each are adjustable. You typically need to adjust it during installation so the water stops where you want. That is shown in the toilet by a mark of some kind inside of the tank. These things adjust in height so they will fit without hitting the tank top. It is pretty simple to install. You may want to replace the line from the shutoff valve to the filler at the same time if it is a flexible one. If it is solid, it will probably be okay, but slight differences in the length of the fitting may mean it is too short or too long.